Device for separating airborne particles in dependence on grain size

ABSTRACT

A device is described for separating airborne particles into classes depending on grain size. The principle characteristic of the present invention lies in the fact that it comprises: 
     a hollow base body, in which, in use, a depression is created; 
     an upper body in which is formed a channel to which there is conveyed, in use, the particle-bearing air and which has a lower extremity with a circular outline; 
     a mesh positioned between the said base body and the said upper body and on which is positioned a filter defining, with the lower face of the said upper body, a cavity; and 
     a nozzle housed in the said channel and operable to eject filtered air in proximity to the said lower end of this latter in such a way that the particles flowing through the said lower end are separated into various bands according to their aerodynamic diameter and are deposited on the said filter.

BACKGROUND OF THE INVENTION

The present invention relates to a device for separating airborneparticles into classes determined by grain size, adapted for use as apersonal sampler able to be carried by the user in order to determinethe risk to the user from inhalations.

As is known, in currently used devices the grain size information isprovided by a pre-selector, which simulates the extrathoracic andtracheo-bronchial passages, and by a filter. In the pre-selector, whichis normally constituted by a cyclone, the particles of larger diameterare deposited, and in the filter the particles of smaller diameter aredeposited.

SUMMARY OF THE INVENTION

The object of the present invention is that of providing a device forseparating airborne particles into grain size classes, in which thetechnique of inertial separation is applied in such a way as to separatethe fraction of the particles having a greater diameter into two grainsize classes in order to obtain a greater amount of information relatingto this latter.

Further objects and advantages will become apparent in the followingdescription.

According to the present invention there is provided a device forseparating airborne particles into grain size classes, characterised bythe fact that it comprises:

a hollow base body in which, in use, there is created a depression bymeans of an external member;

an upper body along the longitudinal axis of which is formed a throughchannel into which is conveyed, in use, the particle-bearing air, andwhich has a lower end of circular outline;

a mesh positioned between the said base body and the said upper body andoperable to support a filter defining, with the lower face of the saidupper body, a cavity which is in good communication through the saidlower end with the said through channel; and

a nozzle in the said channel operable to eject, in proximity to the saidlower end of this latter, filtered air in such a way that in the fluidformed by the particle-bearing air and the filtered air after havingtraversed the said lower end, the particles are separated into variousbands according to their aerodynamic diameter and are deposited on theupper surface of the said filter starting from the particles of greaterdiameter.

DETAILED DESCRIPTION OF THE INVENTION

For a better understanding of the present invention there will now bedescribed a preferred embodiment purely by way of non limitativeexample, with reference to the attached drawing in which there isillustrated a section of the device of the invention, which has beengenerally indicated with the reference numeral 1. This device comprisesa base body 2 formed substantially as a funnel with upwardly facingconcavity. In the lower part of the body 2 there is formed a threadedhole 3 engaged by an upper threaded portion 4 of a pipe union 5 a lowerportion 6 of which, outside the hole 3, supports in use the end of aduct (not illustrated) which can put a pump into communication with theinterior of the body 2 in order to create therein a depression. On theupper edge of the body 2 rests a mesh 8 of circular outline and on thisis deposited a filter 11, also of circular outline. The assemblycomprising the mesh 8 and the filter 11 is pressed between the upperedge of the body 2 and an annular flange 12 extending outwardly from alower end of a sleeve 13 coaxial with but positioned above the body 2.The device 1 further includes a ring 14 which is threaded internally andwhich can be screwed onto a threaded portion 15 of the body 2, formed onthe outer wall thereof. From the upper end of the ring 14 there extends,inwardly, an annular flange 16, and between the lower surface of thislatter and the upper surface of the flange 12 there is disposed asealing ring 17. In use, by screwing the ring 14 onto the portion 15,the flange 16 presses the flange 12 downwardly, which compresses theassembly defined by the filter 11 and the mesh 8 onto the upper edge ofthe body 2. In order to hold the mesh in tension the perimetral edge ofthis extends outwardly between the flange 12 and the upper edge of thebody 2 in such a way that it is drawn downwardly by the inner surface ofthe ring 14 during its screwing onto the portion 15.

As illustrated in the attached drawing, within the sleeve 13 there islodged the lower part of cylindrical body 21 coaxial with the body 2 thelower surface of which faces the filter 11 and is disposed at apredetermined distance therefrom in such a way as to define acylindrical cavity 22. Along the longitudinal axis of the body 21 thereis formed a through channel 23 which opens out at its lower end into thecavity 22 and which has a frusto-conical configuration with the regionof greater diameter located in the uppermost part; the channel 23therefore represents a nozzle which injects an aerosol into the cavity22. For this purpose the channel 23 has a lower end, hereinafter termedthe outlet end and indicated with 23', which has no sharp corners sincethese have been suitably rounded.

On the upper face of the body 21 there is fixed, by screws 25, a plate26 of circular geometry in which there is formed a plurality of throughholes 27 which can put the surrounding air in communication with thechannel 23. Within this latter, and coaxially thereto, there is disposeda nozzle 28 which can inject filtered air in close proximity to theoutlet 23'; the nozzle 28 is fixed to the plate 26, for example bywelding and has an upper end 31 projecting out from the plate 26 andconnected, by means of a connector element 32, with the end of a duct 33which can put the interior of the nozzle 28 into communication with asource of filtered air.

The operation of the device 1 is as follows.

In detail, the said pump creates a depression within the body 2 whichdraws into the channel 23, via the holes 27, the aerosol generated bythe air present in the surrounding environment and particles of dustwhich are in suspension therein. The pump also draws filtered air fromthe said source via the nozzle 28 and the fluid, formed from the aerosoland the filtered air, is drawn into the cavity 22 via the outlet 23'.The technique of inertial separation consists in the fact that theparticles flowing past a sharp curvature, (outlet 23') by intertia tendto maintain their velocity in direction and sense, but are drawn by theflow of fluid; the particles therefore are displaced from the originalstreamline (which flows out downstream of the curvature) by a distancewhich is a function only of the aerodynamic diameter. Consequently theparticles are separated according to diameter into various bands offluid and all the particles of the same grain size will be presentwithin their own streamline; after having traversed the curvature theparticles begin to deposit onto annular portions of the filter 11starting from the particles of greatest diameter. The fluid, cleaned ofthe particles, will subsequently enter into the interior of the body 2towards the pump. Subsequently it is possible to extract the filter 11and perform on the deposit all the chemical and physico chemicalanalyses which are considered necessary for the determination of thetoxicity of the particles in suspension in the air and therefore in theinhalations of the user.

With the device of the invention there is attained on the filter 11 acontinuous deposit of particles and, more precisely, a deposit ofparticles of greater diameter along the central annular portions andgradually of smaller diameter towards the peripheral annular portions ofthe filter 11. In order better to analyse the deposit it is possible tocalibrate the device 1 in such a way as to separate the filter 11 intoseveral parts, for example into three parts, in each of which theretakes place the deposit of particles with a diameter lying within apredetermined interval; for example it is possible to separate thefilter 11 into a first part which is that closest to the outlet 23' inwhich there occurs the deposit of particles with a diameter greater than10 μm., second, central part, in which takes place the deposition ofparticles of the diameter lying between 2.5 or 3.5 μm. and 10 μm., and athird part which is the periphery in which there takes place thedeposition of particles with a diameter less than 2.5 or 3.5 μm. It isapparent that if in the filter 11 there are provided referenceindictions for delimiting the three parts, it is possible to cut thesealong the zones of separation between the various parts and thereforanalyse individually the parts which are of greatest interest or allthree parts to determine the characteristics of the three grain sizefractions into which the particles have been separated. Normally themost interesting part for determining the toxicity of the air which theuser breathes is the second, that is to say that having particles lyingbetween 2.5 or 3.5 μm and 10 μm. The minimum threshold of such part canbe 2.5 or 3.5 μm. according to the sensitivity of the user; the moresensitive the user is the lower the value of the threshold has to be.

It will be evident that the advantages which are obtained with thedevice 1 are those of having provided a portable instrument in which ithas been possible to apply the technique of intertial separation, and ofbeing able to proceed with ease in analysing the deposit sub-dividedinto three grain size classes. It is to be noted that the inertialseparation is assisted by the particular cylindrical geometry of thedevce 1 in that with such geometry, it has been found experimentally, anelongation of the zones of separation between the particles of differentdiameters has been noted and therefore a better and clearer separationof the grain size classes of these. Further, the device is of simpleconstruction and requires no particular maintenance operations, and isof low production costs.

Finally, it is clear that the device described and illustrated here canbe modified and varied without by this departing from the protectivescope of the present invention.

I claim:
 1. A device for separating airborne particles into grain sizeclasses, characterised by the fact that it comprises:a hollow base body(2) in which, in use, there is created a depression by means of anexternal member; an upper body (21) along the longitudinal axis of whichis formed a through channel (23) in which, in use, particle-bearing airis conveyed, and which has a lower end (23') of circular outline; a mesh(8) positioned between the said base body (2) and the said upper body(21) and operable to support a filter (11) defining with the lower faceof the said upper body (21) a cavity (22) which is in communication,through the said lower end (23') with the said through passage (23); anozzle (28) within the said channel (23), operating to eject close tothe lower end (23) of this latter, filtered air in such a way that theparticles in the fluid comprising the particle-bearing air and thefiltered air after having traversed the said lower end (23') areseparated according to their aerodynamic diameter and become depositedon the upper surface of the said filter starting from particles ofgreater diameter.
 2. A device according to claim 1, characterized by thefact that the said nozzle (28) is coaxial with the said channel (23). 3.A device according to claim 2, characterized by the fact that the saidchannel (23) has a cover plate (26) fixed on the upper face of the saidupper body (21); therebeing formed on the said plate (26) at least afirst hole (27) which can put the said channel (23) into communicationwith the environment surrounding the source of particle-bearing air. 4.A device according to claim 3, characterized by the fact that the saidplate (26) supports the said nozzle (28) which is connected by means ofa duct (33) with a source of filtered air.
 5. A device according toclaim 1, characterized by the fact that the said upper body (21) is ofcylindrical configuration and the said base body (2) is formed as afunnel; the said base body (2) having a second threaded hole (3) engagedby an upper portion (4) of a pipe union (5) which can put the saidmember into communication with the interior of the said base body (2).6. A device according to claim 5, characterized by the fact that thesaid mesh (8) and the said filter (11) are of circular geometry.
 7. Adevice according to claim 6, characterized by the fact that the lowerpart of the said upper body (21) is lodged within the interior of asleeve (13) and is supported by this latter; a first annular flange (12)extends outwardly from a lower end of the said sleeve (13) to press theperipheral edge of the assembly comprising the said mesh (8) and thesaid filter (11) onto the edge of the upper end of the said base body(2).
 8. A device according to claim 7, characterized by the fact thatthe upper end of the said base body (2) has an externally threadedlateral portion (15) on which is screwed a ring (14) from the upper endof which extends, inwardly, a second annular flange (16) to press thesaid first flange (12) onto the upper end of the said base body (2). 9.A device according to claim 8, characterized by the fact that a sealingring (17) is disposed between the said first flange (12) and the saidsecond flange (16).